Purpose: We conducted this systematic evidence review of trials of physical activity and/or dietary counseling to prevent cardiovascular disease (CVD) to assist the U.S. Preventive Services Task Force (USPSTF) in updating its 2002 and 2003 recommendations on counseling to improve physical activity and diet, respectively.
Data Sources: We searched MEDLINE, PsycInfo, and the Cochrane Central Register of Controlled Trials 2001–2009 to locate relevant trials for all key questions published since the previous reviews were conducted. We supplemented our searches with suggestions from experts and reference lists from other publications, including the prior USPSTF reviews and other relevant systematic reviews.
Study Selection: Two investigators independently reviewed 13,562 abstracts and 474 articles against a set of a priori inclusion criteria, and also independently critically appraised each study using design-specific quality criteria based on USPSTF methods. Discrepancies were resolved by consensus. In total, 109 articles representing 73 unique studies were included.
Data Extraction and Analysis: One investigator abstracted data from included studies into evidence tables and a second reviewer checked these data. We conducted meta-analyses on 58 trials that provided necessary data to estimate the effect size of counseling on both intermediate health outcomes (adiposity, systolic and diastolic blood pressure, total cholesterol, high-density lipoproteins [HDLs], low-density lipoproteins [LDLs], triglycerides, and glucose) and behavioral outcomes (self-reported physical activity; fitness; intake of total energy, fat, saturated fat, fiber, fruits and vegetables; and urinary sodium as a measure of sodium intake).
Data Synthesis: Key Question 1: Do healthful diet and/or physical activity interventions improve CVD health outcomes in adults? One large, good-quality trial evaluating an intensive healthful diet counseling intervention showed no difference in the incidence of coronary heart disease or stroke over a mean of 8 years followup. Observational followup of two hypertension prevention trials evaluating intensive sodium reduction counseling showed a decrease in the incidence of CVD outcomes over 10 to 15 years of followup.
Key Question 2: Do healthful diet and/or physical activity interventions improve intermediate outcomes associated with CVD in adults? Medium- (31 to 360 minutes) to high-intensity (>360 minutes) dietary interventions (with or without concomitant physical activity counseling) decreased body mass index (BMI) approximately 0.3 to 0.7 kg/m2 at 12 months. The largest reduction in blood pressures occurred in three intensive salt-restriction counseling interventions in persons with mildly elevated diastolic blood pressure, resulting in approximately 1.8 mmHg lower systolic blood pressure and 1.1 mmHg lower diastolic blood pressure at 12 months. Medium- and high-intensity diet and lifestyle interventions decreased systolic blood pressure by 0.9 to 1.4 mmHg and diastolic blood pressure by 0.7 mmHg. Medium- and high-intensity diet and combined lifestyle counseling decreased total cholesterol and LDL. When stratified by intervention intensity, however, this decrease was only significant among the six high-intensity counseling interventions with a reduction in total cholesterol of 0.17 mmol/L (6.56 mg/dL) and LDL by 0.13 mmol/L (5.02 mg/dL). Overall, few trials provided followup longer than 12 months.
Key Question 3: Do healthful diet and/or physical activity interventions change associated health behaviors in adults? Medium- to high-intensity counseling interventions improved self-reported dietary intake of salt, energy, fats, and fruits and vegetables and self-reported physical activity. The medium-intensity physical activity counseling interventions in this review resulted in an approximately 38-minute increase in physical activity per week. Diet and combined lifestyle counseling interventions decreased total fat and saturated fat intake and increased fruit and vegetable consumption. Although there was significant statistical heterogeneity across interventions, there appeared to be an increasing effect size with intervention intensity. Among low-intensity interventions, there was an approximate 1.5 percent decrease in energy intake from fats; for medium-intensity counseling there was an approximate 3.0 to 4.9 percent decrease in energy intake from fats; and for high-intensity interventions there was an approximate 5.9 to 11 percent decrease in energy intake from total fat. Saturated fat intake was reported less frequently, but effects were generally consistent with the magnitude of effect seen with total fat intake. Counseling interventions increased fruit and vegetable intake by approximately 0.4 to 2 servings per day.
Key Question 4: What are the adverse effects of healthful diet and/or physical activity interventions? We found no studies designed to assess the adverse effects of dietary counseling and none of the included healthful diet counseling trials reported specific adverse events. Two physical activity counseling trials reported common findings of mild muscular fatigue, strain, or soreness. Seven comparative observational studies showed that the risk of a cardiac event is increased during vigorous exertion, with a range of 2- to 17-fold increases in risk.
Limitations: In addition to the large statistical heterogeneity limiting confidence in the pooled estimates of effect sizes for some outcomes, other limitations included: there were only 10 trials with followup beyond 12 months, the fact that most trials relied on self-reported behavioral outcomes subject to bias, potential bias due to including only published data, and possible selective reporting of outcomes.
Conclusions: Medium- to high-intensity dietary behavioral counseling resulted in small but statistically significant changes in adiposity, blood pressure, and cholesterol, as well as medium to large changes in self-reported dietary and physical activity behaviors. Evidence for changes in physiologic outcomes was strongest for high-intensity counseling interventions. Medium- to high-intensity physical activity counseling resulted in increases in self-reported physical activity. However, there was limited evidence for maintenance of behavioral or physiologic effects beyond 12 months. Most trials of high-intensity interventions that had followup beyond 12 months showed persistent beneficial changes in adiposity and lipids, as well as improvements in self-reported behavioral outcomes.